Commercial Rooftop Solar ROI in Bangladesh: Payback Period, LCOE & Worked Example

Direct answer: A well-designed commercial rooftop solar plant in Bangladesh typically pays for itself in 3.5 to 6 years. Simple payback equals total project cost divided by annual electricity-bill savings, and factories or offices on the higher BERC tariff bands (e.g. LT commercial at Tk 15.36 per unit under the June 2026 tariff order) sit at the short end of that range, while plants with low daytime consumption sit at the long end.

For a factory owner or commercial-building manager, a rooftop solar proposal is ultimately a financial question: how much money goes in, how much comes back each year, and how soon is the capital recovered. This guide shows exactly how EPC companies in Bangladesh build that calculation, the five inputs that drive it, and a fully worked example for a 100 kWp plant so you can sanity-check any quote you receive.

The five inputs that decide your payback

Every credible ROI model for rooftop solar in Bangladesh stands on the same five pillars:

1. Your retail tariff (Tk/kWh). Each solar unit you consume yourself avoids buying a grid unit at your full tariff. Under BERC's June 2026 tariff order, an LT commercial/office connection pays a flat Tk 15.36 per unit (or Tk 13.82 off-peak / Tk 18.43 peak under time-of-use tariffs), while flat mid-tension commercial connections pay Tk 13.93 and industrial MT consumers pay Tk 12.85. The higher your tariff, the faster your payback — this single input dominates the calculation.
2. Annual generation per kWp. Dhaka's solar resource supports roughly 1,400–1,500 kWh per kWp per year at a healthy performance ratio; a peer-reviewed PVsyst study of a 27 kWp rooftop system in Dhaka measured a specific yield of about 1,341 kWh/kWp/year with a performance ratio of 82.6%. Conservatives model 1,400 kWh/kWp/year.
3. Self-consumption ratio. Units you consume on-site save you the full retail tariff; surplus exported to the grid under net metering is credited at the much lower bulk settlement rate — currently Tk 10.50 per unit paid quarterly. A factory running daytime shifts can self-consume 80–90%; a school empty most afternoons may export much more.
4. Total project cost. Module prices, mounting structure, inverter, AC/DC cabling, metering and installation labour — plus any structural strengthening your roof needs. See our structural assessment guide before assuming a roof is ready.
5. Tariff escalation and degradation. Panel output degrades about 0.5% per year, while BERC has been raising retail tariffs roughly every couple of years (the June 2026 order lifted commercial rates by ~18%). A serious model includes both; the two effects largely offset each other.

The simple-payback formula

Simple payback (years) = Net project cost (Tk)
                         ÷ Annual savings (Tk/year)

Annual savings = (annual kWh × self-consumption share × retail tariff)
               + (annual kWh × export share × export settlement rate)
               − annual O&M and insurance cost

Annual kWh = plant capacity (kWp) × specific yield (kWh/kWp/year). Net project cost means total capex minus any financing subsidy or grant (loans reduce upfront cost but add interest — model them separately as discounted cash flow).

Worked example: 100 kWp factory rooftop

Assume a garments-auxiliary factory in Gazipur with an MT industrial tariff of Tk 12.85 per unit, a 100 kWp array on a shade-free roof, and this conservative set of assumptions:

• Specific yield: 1,400 kWh/kWp/year → 140,000 kWh/year
• Self-consumption: 85% (daytime production load), export 15%
• Export settlement: Tk 10.50/unit
• Project cost: Tk 60,000 per kWp → Tk 6,000,000 total
• Annual O&M + insurance: Tk 120,000

Annual savings = (140,000 × 0.85 × 12.85) + (140,000 × 0.15 × 10.50) − 120,000 = 1,528,450 + 220,500 − 120,000 = Tk 1,628,950 per year

Simple payback = 6,000,000 ÷ 1,628,950 ≈ 3.7 years

After payback, the same plant keeps generating for another 20+ years (modules carry 25-year performance warranties), so lifetime savings are several multiples of the capex. If the tariff rises even once during that period — as the June 2026 BERC revision demonstrates — the actual payback is shorter than the model shows. A board or lender will also ask for discounted payback (typically under 5 years at a 10–12% discount rate) and IRR, both of which this cash-flow profile supports comfortably.

LCOE: the number banks look at

Levelized cost of energy (LCOE) is the all-in cost of each solar unit over the plant's life: total lifetime cost divided by total lifetime generation. For the plant above, Tk 6.0M of capex plus ~25 years of O&M produces roughly 3.3 million kWh — an LCOE around Tk 2.5–3.5 per unit. Compare that with the Tk 12.85 grid tariff you avoid: every self-consumed unit is worth roughly four to five times its generation cost. This is the metric lenders use, and it is why IDCOL and other green financiers treat rooftop solar as bankable. A Dhaka university study (Energies, 2025) computed an LCOE of about US$0.06/kWh (~Tk 7.2) for a 27 kWp Dhaka rooftop system with a sub-five-year payback — same order of magnitude, independently confirmed.

What shortens or lengthens payback

• Daytime load profile: a cold storage running 24/7 or a daytime factory captures the full tariff value of every unit; a plant idle at noon exports cheap surplus. Size the array to your load, not to your roof — our hybrid vs on-grid comparison explains the trade-offs.
• Tariff band: commercial LT at Tk 15.36 pays back ~20% faster than industrial MT at Tk 12.85 for the same plant cost.
• Design quality: correct DC cable sizing, right tilt and row spacing, and clean panels decide whether you get 1,300 or 1,500 kWh/kWp/year. A 10% yield shortfall stretches payback by roughly a year.
• Monitoring: a plant you watch stays healthy; one you ignore drifts. Track performance ratio and availability monthly.

FAQs

How long is the payback for a 50 kWp office rooftop in Dhaka?

On the LT commercial flat tariff of Tk 15.36 per unit with 85% self-consumption and typical capex, expect about 3 to 3.5 years — offices score the fastest payback of any consumer class because they pay the highest tariffs and use power exactly when panels produce.

Does net metering surplus payment change the math much?

At Tk 10.50 per unit paid quarterly, surplus export contributes but is worth far less than self-consumption at Tk 12–15 per unit. Design for high self-consumption first; treat export credits as a bonus, not the business case.

Should I include battery backup in the ROI calculation?

Only if you need it. Batteries add significant capex and degrade the payback — pure grid-tied net-metered systems pay back fastest. Add storage only for critical loads or diesel displacement, as discussed in our BESS guide.

What does IDCOL financing do to the numbers?

Green refinancing replaces upfront capex with loan instalments. It lowers the initial outlay and can make the project cash-positive from year one, but interest raises the total cost — always compare the financed payback against the self-financed one.